The present invention relates to the field of mass storage devices. More particularly, this invention relates to an apparatus and method for moving a transducing head within a disc drive from a first track to a second track. The operation of moving a transducing head from a first track to a second track is commonly called a seek.
One key component of any computer system is a device to store data. Computer systems have many different places where data can be stored. One conmmon place for storing massive amounts of data in a computer system is on a disc drive. The most basic parts of a disc drive are an information storage disc that is rotated, an actuator that moves a transducer to various locations over the disc, and electrical circuitry that is used to write and read data to and from the disc. The disc drive also includes circuitry for encoding data so that it can be successfully retrieved and written to the disc surface. A microprocessor controls most of the operations of the disc drive as well as passing the data back to the requesting computer and taking data from a requesting computer for storing to the disc.
The transducer is typically placed on a small ceramic block, also referred to as a slider, that is aerodynamically designed so that it flies over the disc. The slider is passed over the disc in a transducing relationship with the disc. Most sliders have an air-bearing surface (xe2x80x9cABSxe2x80x9d) which includes rails and a cavity between the rails. When the disc rotates, air is dragged between the rails and the disc surface causing pressure, which forces the head away from the disc. At the same time, the air rushing past the cavity or depression in the air bearing surface produces a negative pressure area The negative pressure or suction counteracts the pressure produced at the rails. The slider is also attached to a load spring which produces a force on the slider directed toward the disc surface. The various forces equilibrate so the slider flies over the surface of the disc at a particalar desired fly height. Tile fly height is the distance between the disc surface and the transducing head, which is typically the thickness of the air lubrication film. This film eliminates the friction and resulting wear that would occur if the transducing head and disc were in mechanical contact during disc rotation in some disc drives, the slider passes through a layer of lubricant rather than flying over the surface of the disc.
Information representative of data is stored on the surface of the storage disc. Disc drive systems read and write information stored on tracks on storage discs. Transducers, in the form of read/write heads attached to the sliders, located on both sides of the storage disc, read and write information on the storage discs when the transducers are accurately positioned over one of the designated tracks on the surface of the storage disc. The transducer is also said to be moved to a target track. As the storage disc spins and the read/write head is accurately positioned above a target track, the read/write head can store data onto a track by writing information representative of data onto the storage disc Similarly, reading data on a storage disc is accomplished by positioning the read/write head above a target track and reading the stored material on the storage disc. To write on or read from different tracks, the read/write head is moved radially across the tracks to a selected target track.
The methods for positioning the transducer can generally be grouped into two categories Disc drives with linear actuators move the transducer linearly generally along a radial line to position the transducers over the various tracks on the information storage disc. Disc drives also have rotary actuators which are mounted to the base of the disc drive for arcuate movement of the transducers across the tracks of the information storage disc. Rotary actuators position transducers by rotationally moving them to a specified location on an information recording disc. A rotary actuator positions the transducer quickly and precisely.
The actuator is rotatably attached to a shaft via a bearing cartridge which generally includes one or more sets of ball bearings. The shaft is attached to the base and may be attached to the top cover of the disc drive. A yoke is attached to the actuator. The voice coil is attached to the yoke at one end of the rotary actuator. The voice coil is part of a voice coil motor which is used to rotate the actuator and the attached transducer or transducers. A permanent magnet is attached to the base and cover of the disc drive. The voice coil motor which drives the rotary actuator comprises the voice coil and the permanent magnet. The voice coil is attached to the rotary actuator and the permanent magnet is fixed on the base. A yoke is generally used to attach the permanent magnet to the base and to direct the flux of the permanent magnet. Since the voice coil sandwiched between the magnet and yoke assembly is subjected to magnetic fields, electricity can be applied to the voice coil to drive it so as to position the transducers at a target track.
Quick and precise positioning requires the reduction of the vibration of the magnetic disc apparatus caused by the driving reaction force to the voice coil motor. What is needed is a disc drive which is less susceptible to the reaction forces. This will improve settling characteristics after a seek from a first track on the disc to a target track on the disc and will improve track following operations of the disc drive. In other words, there is a need for a disc drive that has less relative motion between the actuator assembly and the base while under any type of servo control that requires corrections to be implemented with the voice coil motor. There is also a need For a static solution so that the resulting disc drive is more reliable over the life of the drive. Also needed is a device that can be assembled using current assembly techniques.
One constant goal associated with disc drives is to decrease or lessen the access time to data. Increasing the speed at which data can be retrieved is very desirable in a disc drive. The decrease in access time increases the speed at which a computer system can perform operations on data. When a computer is commanded to perform an operation on data or information that needs to be retrieved, the time necessary to retrieve the data from the disc is generally the bottleneck in the operation. When data is accessed more quickly, more transactions can generally be handled by a computer in a particular unit of time.
Most of the methods for control access time include referring to a velocity profile. A velocity profile is a pre-programmed equation or table which lists a desired velocity verses the stopping distance remaining until reaching the target track. In other words, a velocity profile provides the velocity the transducer head should have at varying distances from the destination or target track and, at each of a succession of tracks terminating with the destination or target track. Generally, the profile velocity value is the highest possible value of velocity the actuator can have at a particular remaining distance to allow the actuator to be decelerated to a stop upon reaching the destination or target track. Of course, there may be factors, such as power savings, that may steer designers away from following the highest possible velocity.
The velocity profile is shaped with respect to the number of tracks remaining in a seek to cause the transducer head to initially accelerate toward the destination or target track and subsequently decelerate to the destination or target track. In long seeks, these stages of the seek may be separated by a stage in which the transducer head traverses a series of tracks at a maximum speed that is selected on the basis of any of a number of criteria used by the manufacturer of the disk drive. For example, the maximum speed may be chosen to be the maximum speed the transducer head can attain with the power supply that is used to operate the servo system. A control signal is provided to the power amplifier that is directly proportional to the difference between the profile velocity and the actual velocity of the transducer head.
A typical seek is accomplished using closed loop control. The distance left to go to the destination or target track is determined and then the corresponding velocity from the velocity profile is selected. The difference between the actual actuator velocity and profile actuator velocity is provided to the servo controller. This value is then multiplied by a gain to give a control current output to the voice coil.
When the profile velocity is larger than the actual velocity, the result of subtracting actual actuator velocity from the selected velocity obtained from the velocity profile is positive, and the actuator is accelerated When the profile velocity is less than actual velocity, the result of subtracting actual actuator velocity from the selected velocity form the velocity profile is negative, and the actuator is decelerated. The gain is chosen in the closed loop control method so that it is as high as possible yet still within the limits of stability and such that good conformity to the velocity profile is achieved.
The use of a velocity profile that can be developed with respect to any selected servo system operating criteria can be used to minimize the time required for the seek to occur and still reach the destination track with a speed that is neither too large nor too small to effectuate a rapid settling of the transducer bead on the destination track at the end of the seek. Specifically, since the control signal is proportional to the difference between the profile velocity and the actual velocity, the transducer bead can be caused to rapidly accelerate at the beginning of the seek by providing a profile that calls for large velocities at the beginning of the seek and then rapidly tapering the profile to zero as the destination track is reached.
The amount of deceleration that can be applied to the actuator is a function of many variables including voice coil resistance file torque constant and power supply voltage. These variables are generally not known for each specific file and as a result, the velocity profile is designed using worst case values to assure that there will always be adequate deceleration capability to stop the actuator upon reaching the target track.
Due to manufacturing tolerances of all the parts that are assembled to form an actuator, it turns out that each transducer on each arm has a different seek time for a given length of seek. For example, different load beams and flexures have different settling times. One of the shortcomings associated with prior seek methods is that the velocity profile is designed to accommodate the slowest seek time of the transducer heads in a population of disc drives. This assumes the worst case conditions so that adequate margin is available for both acceleration and deceleration for a given velocity profile. As a result, all of the disc drives operate under worst case conditions at less than an optimal level. In other words, the actuators operate at suboptimal velocities rather than operating a more optimal velocity.
What is needed is a seek procedure that allows for faster seeks. What is also needed is a seek procedure which can be accommodated using manufacturing techniques close to current manufacturing techniques.
A disc drive includes a base and a disc rotatably attached to the base. The disc drive also includes an actuator assembly rotatably attached to said base and a device for moving the actuator assembly. The disc drive includes servo circuitry and a controller for controlling movement of the actuator during track follow and track seek operations. The controller also controls head switches between various transducing heads in the disc drive. The disc drive determines the average seek time for each head and also measures the amount of time for a head switch from the transducer head having the shortest average seek time to all the other transducing heads in the disc drive. When a seek is performed, the controller in the disc drive determines if the shortest average seek time plus the seek time from the transducing head to the transducing bead on the surface containing the target track and sector is less than the average seek time of the head on the surface having the target track and sector. If the shortest average seek time and the head switch time is less than the average seek time of the head on the surface, the controller uses the head with the shortest average seek time to perform the seek and then switches to the transducing head associated with the target or destination track so that the information under that head can be read.
The disc drive controls the movement of an actuator in a disk drive from a first track to a second track on a target surface. The actuator has a plurality of transducers attached to a plurality of arms of the actuator. The method includes determining the average access times for each of the transducing heads in the disc drive, and measuring the amount of time for a head switch from each of the plurality of transducing heads to the transducing head of the plurality of transducing heads having the shortest average access time. The average seek time associated with a transducing head on a target surface is compared to an amount of time associated with the average seek time of the transducing head having the shortest average seek time plus a head switch from the transducing head with the shortest average access time to the transducing head on the target track. A seek may be performed with a transducing head other than the transducing head associated with the target surface. Such a seek is performed when the amount of time associated with the average seek time of the transducing head on the target surface plus a head switch from the transducing head with the shortest average access time is less than the average seek time associated with a transducing head having the shortest average seek time.
The comparison further includes storing the average seek times of each head on a table and determining the transducing head with the shortest average seek time and performing head switches between the head with the shortest average seek time and each of the other transducing heads in the disc drive. In addition a value is stored for each of the other transducing heads equal to the average seek time for a particular head plus the head switch time between the particular transducer head and the tansducer head with the shortest average seek time. The value for each of the transducing head may be stored in a lookup table in memory or on the disc. If on the disc, the lookup table is stored at a reserve area on one of the plurality of discs. When the lookup table is stored at a reserve area on one of the plurality of discs, the information is uploaded from the disc to memory
Also disclosed is a disc drive having a base, a disc rotatably attached to the base. Servo information is stored on each of the surfaces of the disc. One of said surfaces of the disc has a first track and a second track. The other of said surfaces has a third track and a fourth track An actuator has a first transducer for reading and writing to the first and second track and a second transducer for reading and writing to the third and fourth track. A computer usable storage medium, having control information stored thereon for causes a suitably programmed disc drive to seek from a first track on the disc to a second track on a disc using the transducer for reading the third and fourth track on the disc. The computer usable storage medium performs the following steps: seeking between the third and fourth tracks with the second transducer head, and switching from the second transducer head to the first transducer head. The computer usable storage medium stores control information indicating when the time associated with seeking between the third and fourth tracks with the second transducer and switching from the second transducer to the first transducer is faster than seeking between the first and second tracks with the first transducer. The computer usable storage medium controls servo circuitry to seek between the third and fourth tracks and switch to the first transducer when it will be faster than seeking between the first and second tracks with the first transducer. The first and third tracks are within a first cylinder and the second and fourth tracks are within a second cylinder. The control information in the computer usable storage medium includes using the servo circuitry within the disc drive. The servo circuitry within the disc drive is to determine if a seek can be performed in the disc drive between a first cylinder containing the first track and the third track and the a second cylinder containing the second track and the fourth track in less time when seeking between the third track and the fourth track than between the first track and the second track. This can be done at the time of manufacture.
Also disclosed is a disc drive including a base and an actuator rotatably attached to the base. The actuator has a first end and a second end and further includes a transducing head attached to the other of the first or second ends of the actuator. At least one disc is rotatably attached to the base. The disc has a first surface and a second surface. The invention includes a device for performing a seek between tracks on a first surface while using information stored on the second surface and the transducing head on the second surface.
Advantageously, the seek procedure set forth above and the apparatus for implementing the seek procedure allow for faster seeks. The seek procedure can be incorporated in microcode and used to control the servo circuitry to implement the invention. The information needed can easily be obtained during the manufacture of the disc drive. Obtaining the information needed can be accomplished without deviating substantially from manufacturing techniques close to current manufacturing techniques. The end result will be a reduction in access times to data.